Defects in DNA ligase I trigger PCNA ubiquitylation at Lys 107
Defects in DNA ligase I trigger PCNA ubiquitylation at Lys 107
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DOI：
10.1038/ncb2007
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发表时间：
2010-01-01
影响因子：
21.3
通讯作者：
Bielinsky, Anja-Katrin
中科院分区：
文献类型：
--
作者：
Das-Bradoo, Sapna;Nguyen, Hai Dang;Bielinsky, Anja-Katrin
在所有真核生物中，新合成的 DNA（也称为冈崎片段）的连接是由 DNA 连接酶 I 催化的（参考文献 1）。 DNA 连接酶 I 缺陷的个体会表现出生长迟缓、阳光敏感性和严重的免疫抑制(2)，这可能是由于 DNA 损伤的累积所致。令人惊讶的是，人们对 DNA 连接酶 I 缺陷细胞中的 DNA 损伤反应 (DDR) 知之甚少。由于DNA复制和DDR途径在真核生物中高度保守，我们使用酿酒酵母作为模型系统来解决这个问题。我们发现了一条新途径，可促进增殖细胞核抗原 (PCNA) 第 107 位赖氨酸的泛素化。与 PCNA 的第 164 位赖氨酸泛素化响应 UV 照射而引发跨损伤合成 (3) 不同，Lys 107 的修饰不依赖于泛素缀合酶 (E2) Rad6（参考文献 4）也不依赖于泛素连接酶 (E3) Rad18（参考文献 5），而是需要 E2 变体 Mms2（参考文献 6）与 Ubc4（参考文献 6）结合。 7) 和 E3 Rad5（参考文献 8、9）。令人惊讶的是，DNA 连接酶 I 缺陷且携带 PCNA(K107R) 突变的酿酒酵母 cdc9-1 细胞无法存活，因为它们无法激活强大的 DDR。此外，我们发现，DNA 连接酶 I 缺陷引起的 PCNA 泛素化在人类中是保守的，但被修饰的赖氨酸残基仍有待确定。我们提出 PCNA 泛素化提供了“DNA 损伤代码”，使细胞能够对 DNA 复制过程中出现的不同类型的缺陷进行分类。
In all eukaryotes, the ligation of newly synthesized DNA, also known as Okazaki fragments, is catalysed by DNA ligase I (ref. 1). An individual with a DNA ligase I deficiency exhibits growth retardation, sunlight sensitivity and severe immunosuppression(2), probably due to accumulation of DNA damage. Surprisingly, not much is known about the DNA damage response (DDR) in DNA ligase I-deficient cells. As DNA replication and DDR pathways are highly conserved in eukaryotes, we used Saccharomyces cerevisiae as a model system to address this issue. We uncovered a new pathway, which facilitates ubiquitylation at Lys 107 of proliferating cell nuclear antigen (PCNA). Unlike ubiquitylation at Lys 164 of PCNA in response to UV irradiation, which triggers translesion synthesis(3), modification of Lys 107 is not dependent on the ubiquitin conjugating enzyme (E2) Rad6 (ref. 4) nor the ubiquitin ligase (E3) Rad18 (ref. 5), but requires the E2 variant Mms2 (ref. 6) in conjunction with Ubc4 (ref. 7) and the E3 Rad5 (refs 8, 9). Surprisingly, DNA ligase I-deficient S. cerevisiae cdc9-1 cells that carry a PCNA(K107R) mutation are inviable, because they cannot activate a robust DDR. Furthermore, we show that ubiquitylation of PCNA in response to DNA ligase I deficiency is conserved in humans, yet the lysine residue that is modified remains to be determined. We propose that PCNA ubiquitylation provides a 'DNA damage code' that allows cells to categorize different types of defects that arise during DNA replication.